1. Field of the Invention
This invention, in general, relates to the field of body implantable leads for the electrical stimulation of living tissue, and more particularly concerns a lead having a ring electrode with a barrel shape for improved contact with body tissue which, at the same time, functions to mechanically weld the various parts of the lead together and which can be made in a simplified manufacturing process.
2. Description of the Prior Art
Electrical stimulation of the body is an increasingly important medical procedure. For example, electrical stimulation of the heart is now the preferred medical procedure for treating heart block, as well as other types of heart malfunction, and electrical stimulation of the spinal cord has proven to be effective in relieving chronic pain. Generally the leads used in such biomedical stimulation contexts comprise an exposed electrode for making electrical contact with the body tissues and a lead body, which includes a conductor electrically connected to the electrode and an insulating casing enclosing the conductor and forming the external portion of the lead body. Generally, the casing is made of a pliable material generally inert to body fluids, such as polyurethane, silicone rubber or the like.
The electrode in many of such lead applications comprises a conducting band encircling the lead body and conventionally is called a ring electrode. Generally such an electrode is of the form of a right-circular cylinder made of platinum or any similar material which is highly conductive and resistant to body fluid. Examples of such ring electrodes are disclosed in U.S. Pat. No. 4,280,511 for a Ring Electrode for Pacing Lead and Process of Making Same invented by Edward G. O'Neill and U.S. Pat. No. 4,328,812 entitled Ring Electrode for Pacing Lead and an invention of Keith A. Ufford and Edward G. O'Neill, U.S. Pat. No. 4,328,812 discloses a ring electrode in which the diameter of the ring cylinder is greater than the diameter of the lead casing (except for a small portion of the casing adjacent the electrode which has the same diameter as the ring electrode). This places the surface of the ring in closer relation to the body tissue than the casing is generally, thereby improving electrical contact with the tissue. However, in order to ensure that body fluids do not penetrate the juncture of the ring electrode and the lead body, and to ensure good electrical connection between the electrode and conductor, the structure of the electrical connection is quite complex. U.S. Pat. No. 4,280,511 shows a simplified ring structure and a simplified method of manufacture of the lead with the ring electrode. The diameter of the ring electrode in this latter disclosure is the same as the diameter of the lead body.